Idea: Add an input allowing fully customizable mixing schedules

[ttulttul]

There are currently three mixing schedules available: linear, cosine, and logistic. It's possible that other mixing strategies could produce interesting results, such as completely non-linear schedules or schedules that involve randomness. You could for instance mix z_prime only during 25% of the steps. Our node here should allow for another input that can receive a mixing schedule as a tensor that could be produced by other nodes.